C3+ olefins, particularly C3+ iso-olefins, can be used to produce many useful products. For example, isobutene can be used to produce polyisobutylene, which in turn is used to produce butyl rubber. Isobutene is generally obtained from a mixture of C4 olefins (e.g., 1-butene, 2-butenes). Separating isobutene from the mixture by distillation is difficult because C4 olefins have similar boiling points at atmospheric pressure (“atmospheric boiling point”).
U.S. Pat. Nos. 3,121,124; 3,270,081; 3,170,000; and 4,307,254, disclose methods for overcoming this difficulty, e.g., by (i) converting isobutene into a derivative which can be more easily separated from the remaining hydrocarbons in the mixture and then (ii) converting the isolated derivative back to isobutene. The process can utilize an acidic catalyst, as disclosed in U.S. Pat. Nos. 2,720,547 and 4,219,678. The process can be conducted in a single reactor, or in a plurality of reactors as disclosed in U.S. Pat. No. 3,979,461.
One conventional process, disclosed in U.S. Pat. No. 7,910,786, involves obtaining a C4 olefin fraction from hydrocarbon cracking processes such as steam cracking and catalytic cracking. The patent discloses removing multiple-unsaturated hydrocarbons, mainly butadiene, and then reacting the remaining mixture (identified as raffinate I or hydrogenated cracking C4) with methanol to produce methyl tert-butyl ether (“MTBE”) from the mixture's isobutene. The MTBE is then separated from the remainder of the C4 mixture, and converted to isobutene and methanol. U.S. Pat. No. 4,307,254 discloses producing the MTBE in a catalytic distillation reactor. Besides decomposing MTBE to produce isobutene, it is also conventional to utilize MTBE as a blendstock for increasing the oxygenate content of gasoline.
Besides their use for producing MTBE and isobutene, C3+ olefins can also be utilized for producing di-C3+ olefin, such as diisobutylene, which can be blended into gasoline to increase the gasoline's octane number, as disclosed in U.S. Pat. No. 7,473,812.
In cases where (i) alternative oxygenates, such as ethanol are utilized, in place of MTBE for increasing gasoline oxygenate content, and/or (ii) there is insufficient need for the isobutene produced by MTBE decomposition, it would be desirable to simultaneously produce C4+ ether and di-C3+ olefin from a C3+ olefin mixture. Moreover, it would be desirable to configure such a process so that the relative amounts of the ether and di-C3+ olefin could be varied, e.g., to meet isobutylene demand.